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Re: smmu-related clarification


  • To: Jorge Pereira <jorge.pereira@xxxxxxx>
  • From: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
  • Date: Thu, 19 Nov 2020 15:25:34 +0000
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  • Delivery-date: Thu, 19 Nov 2020 15:26:18 +0000
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  • Thread-topic: smmu-related clarification

Hi Jorge,

> On 19 Nov 2020, at 13:16, Jorge Pereira <jorge.pereira@xxxxxxx> wrote:
> 
> Hi All,
>  
> I’m having some smmu-related issues, I need help. 
>  
> So, in my use-case scenario I have two linux guests running in parallel – 
> dom0 and domU-. I have to enable the smmu because I want to passthough 
> devices to domU.
>  
> Would be great if you help me to clarify the following questions:  
>       • if I enable SMMU, it will applies not only to domU but also to 
> dma-capable devices assigned to dom0?

yes it will apply to all your domains.

>       • Do I have to add all smmu-masters  of dom0 in device tree as well? Or 
> since dom0 has 1:1 mapping I don’t have to do anything?

smmu is not only used for remapping but also to protect DMA accesses which 
means for dom0 it will use 1:1 mapping but will limit DMA to the memory 
accessible to dom0.
So you will need to add all required smmu information to all devices you need 
otherwise devices will be denied any DMA access.

Regards
Bertrand

>  
> Thanks,
> Jorge


 


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